1. Field of the Invention
The present invention relates generally to an interchangeable lens mountable into a camera body of a lens interchangeable type and to a camera system incorporating this interchangeable lens. This invention relates more particularly to an interchangeable lens including a focal detector and to a camera system incorporating this interchangeable lens.
2. Related Background Art
A conventional focal detector built-in interchangeable lens is disclosed in, e.g., Japanese Patent Application Laid-open No. 59-128506. This interchangeable lens is of such a type that an elongate mirror is disposed with a tilt in a location apart from the optical axis within a light path of the interchangeable lens, and the light reflected by this mirror is led to a focal detector.
In the conventional focal detector built-in interchangeable lens described above, however, as shown in FIG. 6, a mirror 2 for leading some of a bundle of incident rays to a focal detector 1 is fixedly provided. The rays incident on the interchangeable lens are cut off by this mirror 2. For this reason, only doughnut-like rays T indicated by oblique lines in the Figure reach a focal surface 9a of the interchangeable lens 9. There arises such a problem that the actual brightness becomes lower than a brightness of the interchangeable lens. Then, the doughnut-like rays are projected on a film surface of an out-of-focus portion of a subject, i.e., on a focal surface 9b when defocused. Consequently, there is produced a problem in which a doughnut-like blur is formed in the case of projecting the rays T on the film surface 9b when defocused; and this blur is an extreme eyesore.
Further, as illustrated in FIG. 7, the rays passing through the interchangeable lens are incident on a focal detector (AF module 14) incorporated into a conventional camera body via a quick return mirror 13A and an auxiliary mirror 13B. Then, when this AF module 14 detects a focal point of a reflex telephoto lens, a bundle of rays S incident on the reflex telephoto lens are partly cut off by a submirror 6A. It is therefore impossible to perform a precise focal detection. Besides, this AF module 14 detects the focal point of the interchangeable lens other than the above-described reflex telephoto lens. In this case also, if a full-aperture F-number of this interchangeable lens is large, the rays incident on the interchangeable lens are partly cut off by a metal frame and a fixed stop of the interchangeable lens. The precise focal detection can not be therefore performed. The reason for this will be elucidated. Respective bundles of rays reaching the individual light receiving elements are partly cut off by a pair of image-reforming lenses provided in the AF module 14. Hereupon, there arises a possibility wherein a symmetry of the rays is lost, and a correlation can not be taken by the pair of light receiving elements. It is therefore impossible to precisely detect the focal point.